The present invention relates to an apparatus and process for injection molding plastic material and particularly a nozzle assembly used in a hot runner assembly system and through which plastic material flows.
Typical hot runner nozzle assemblies include a nozzle body that has a heater in heat exchange relationship with respect thereto. It is generally necessary to disassemble the mold in order to replace or repair the heaters. This represents a time consuming and expensive procedure. Fast and easy serviceability are highly desirable in these systems.
The present invention provides an improved system and process which permits the convenient removal and replacement or repair of the nozzle body and heater without disassembly of the mold.
U.S. Pat. No. 5,374,182 to Gessner shows a nozzle assembly with a heater clamped to the exterior of the nozzle housing and providing a means for replacing the heater. The mold plate is latched over in the molding machine, thereby permitting exposure of the heater and providing access for its removal from the nozzle body.
U.S. Pat. No. 4,768,945 to Schmidt shows a nozzle assembly having a heater embedded into the nozzle body. It is well known that during the operation of the injection mold the nozzle heater may burn out. However, in order to replace the heater by removing the nozzle body so that a new heater can be installed, the mold must be disassembled so that the entire nozzle assembly can be removed. This is a time consuming and costly process which severely impacts the productivity of the mold.
U.S. Pat. No. 3,553,788 to Putkowski uses a hot runner nozzle assembly with a nozzle body that has a sliding fit connection to the hot runner manifold and the gate pad. The housing has an external heater clamped to its exterior. The sliding fit is designed to accommodate thermal expansion of the nozzle body as it is heated. The design relies on the sliding fit not leaking plastic when subjected to high plastic injection pressure inside the melt channel. However, replacement of the heater without dismantling the mold is difficult because the heater wiring is routed via the air space surrounding the hot runner manifold and is not accessible by removal of the cavity plate. Furthermore, sliding fit style hot runners tend to leak plastic when pressurized.
U.S. Pat. No. 4,095,931 shows a hot runner nozzle assembly with a heated nozzle assembly wherein both an outer sheath and an inner sleeve can be removed by unthreading them from the nozzle header and thereby exposing the heater. However, the wiring to the heater is routed through the nozzle header making it difficult to replace the heater without the expense and inconvenience of dismantling more of the nozzle assembly.
U.S. Pat. No. 3,295,169 to Moslo shows a heated machine nozzle with heaters clamped externally to a threaded, removable outer nozzle sleeve. There is no teaching of how this nozzle could be incorporated in a mold structure. In addition, these heaters do not transfer heat as efficiently as an integral heating element. Also, positioning of the heater in tight spaces can be a problem as they tend to be bulky.
U.S. Pat. No. 4,303,169 shows a nozzle tip portion which is screwed onto a heated body. An insulating bushing centrally locates the nozzle in the mold plate. However, in order to remove the heated portion, or even the nozzle tip, the mold plate must be disassembled from the hot runner.
Accordingly, it is a principal object of the present invention to provide an improved apparatus and method including a nozzle assembly with a nozzle body and heating means wherein the nozzle body and heating means may be simply, conveniently and expeditiously removed for replacement or repair of the heating means.
Further objects and advantages of the present invention will appear hereinbelow.